1. Field of the Invention
The present invention relates to a semiconductor device manufacturing method of calculating an optimum exposure value from the size of a photolithographed pattern in a transfer process for semiconductor manufacturing, and controlling the exposure value by feeding back the calculated value. The present invention also relates to a system for implementing the manufacturing method, and a semiconductor device manufactured by the manufacturing method.
2. Description of the Background Art
In general, a photolithographic process is intended to apply a photosensitive material to a wafer, expose the photosensitive material by an exposure device for development, and thereby form a pattern. Thereafter, the size of the formed pattern is measured. For the size measurement, a target value and a standard value are set, and the finished pattern is considered to be better as the size measurement result is closer to the target value.
In the conventional photolithographic process as described above, the exposure step is carried out by first setting an exposure value and maintaining the exposure value to be constant. However, an optimum exposure value for performing a patterning step in the photolithographic process is varied by various factors such as change in the underlying layer or fluctuation in the exposure device. If the exposure value is controlled to be constant, therefore, the set exposure value may deviate from the optimum exposure value due to change in the underlying layer, for example. In this case, the size measurement result of the developed pattern deviates from the target value.
In order to solve this problem, an operator may change the exposure value by resetting the optimum exposure value when the size measurement result deviates from the target value. In this case, however, the conditions need to be reset and a delay is caused until the optimum exposure value is reflected.
The present invention was made to solve the above described problems. An object of the present invention is to easily correct an exposure value to an optimum exposure value at an early stage even if change in the underlying layer, fluctuation in the exposure device or the like is caused, by performing the exposure operation at an optimum exposure value which is calculated automatically by utilizing a size measurement result.
A semiconductor manufacturing system according to the present invention includes exposure value detection means for detecting the exposure value of an exposure device, pattern size detection means for detecting the size of a pattern formed after photolithography, size comparison means for comparing the pattern size detected by the pattern size detection means and a target value to calculate a size difference, optimum exposure value calculation means for calculating an optimum exposure value by using the size difference and the exposure value, and exposure value control means for controlling the exposure value of the exposure device so as to be the optimum exposure value calculated by the optimum exposure value calculation means.
By providing the exposure value detection means and the pattern size detection means as described above, the exposure value of the exposure device and the size of the pattern formed after photolithography can be detected. By providing the size comparison means, the size difference between the pattern size and the target value can be calculated. By using the size difference and the exposure value, the optimum exposure value calculation means can automatically calculate the optimum exposure value. The exposure value control means can control the exposure value of the exposure device so as to be the optimum exposure value calculated as described above. Even if change in the underlying layer, fluctuation in the exposure device or the like is caused, an exposure operation at an optimum exposure value can be performed by changing the exposure value at an early stage and in a simple manner. Specifically, wafers of the next lot can be exposed at the optimum exposure value.
The above described exposure value calculation means may calculate the optimum exposure value by adding a product of a conversion coefficient for the pattern by the size difference to an actual exposure value. In this specification, the conversion coefficient is a coefficient for converting a size to an exposure value, and a variable exposure value can be calculated by multiplying a conversion coefficient by a variable size.
For example, the above described conversion coefficient can be found for each pattern based on a correlation of the size difference with a difference between the optimum exposure value and the actual exposure value. By multiplying the conversion coefficient by the size difference, it is possible to obtain the difference between the actual exposure value and the optimum exposure value. By adding the difference to the actual exposure value, the optimum exposure value can be calculated.
When a plurality of patterns are formed, the optimum exposure value calculation means calculates a product of the conversion coefficient and the size difference for each pattern. The optimum exposure value calculation means has at least one operation means selected from the group of first operation means for finding an average value of the product values for the patterns, second operation means for selecting a central value of the product values for the patterns when the products are arranged in order of magnitude, and third operation means for multiplying the product values for the patterns by coefficients according to the patterns, adding them together and dividing the result by a sum of the coefficients.
The first operation means can control the size of each pattern so as to be the average value of the sizes of the plurality of patterns. The second operation means can control the size of each pattern so as to be the central value of the sizes of the plurality of patterns. The third operation means can control the size of each pattern so as to be a result of weighting the size of a desired pattern of the plurality of patterns.
The semiconductor manufacturing system of the present invention preferably includes pattern selection means for selecting a desired pattern among a plurality of patterns when the plurality of patterns are formed.
Thus, the optimum exposure value can be calculated by paying attention only to an important pattern, for example. Furthermore, the optimum exposure value can be calculated by paying attention only to a pattern at a prescribed position.
The pattern may be a developed pattern (pattern of a photosensitive material, for example) formed by development. In this case, the size comparison means compares the size of the developed pattern and a target value to calculate a size difference.
By using the size of the developed pattern as described above, the optimum exposure value can be calculated at an earlier stage as compared with a case where an etched pattern, described below, is used.
Meanwhile, the pattern may be an etched pattern formed by etching. In this case, the size comparison means compares the size of the etched pattern and a target value to calculate a size difference. It is noted that the etched pattern includes a pattern which is formed by etching a conductive layer, an insulation layer or the like using a developed pattern, for example, as a mask.
By using the pattern size after etching as described above, fluctuations in the etching manner can be addressed.
The semiconductor manufacturing system of the present invention preferably includes data storage means for storing the exposure value, the pattern size, the size difference and the optimum exposure value.
Thus, past data can be effectively utilized if necessary, and the optimum exposure value can be calculated easily. Even when a new pattern is to be formed, the optimum exposure value can be determined based on the above described data.
A semiconductor device manufacturing method of the present invention includes the steps of applying a photosensitive material, exposing the photosensitive material by an exposure device, detecting the exposure value of the exposure device during the exposing step, developing the photosensitive material, detecting the size of a pattern formed after development, comparing the detected size of the pattern and a target value to calculate a size difference, calculating an optimum exposure value by using the size difference and the exposure value, and controlling the exposure value of the exposure device so as to be the optimum exposure value.
By detecting the exposure value of the exposure device and comparing the size of the pattern formed after development and the target value to calculate the size difference as described above, the optimum exposure value can be automatically calculated by using these values. By controlling the exposure value of the exposure device so as to be the optimum exposure value calculated as described above, exposure at the optimum exposure value can be performed at an early stage even if change in the underlying layer, fluctuation in the exposure device or the like is caused.
Similarly to the case of the above described semiconductor manufacturing system, the optimum exposure value may be calculated by adding a product of a conversion coefficient for the pattern by the size difference to the exposure value. When a plurality of patterns are formed, the product value of the conversion coefficient by the size difference may be an average value of the product values for the patterns, a central value of the product values for the patterns when the products are arranged in order of magnitude, or a value which is obtained by multiplying the product values for the patterns by coefficients according to the patterns, adding them together and dividing the result by a sum of the coefficients. Thus, similar effects to the case of the semiconductor manufacturing system can be expected.
When a plurality of patterns are formed, the semiconductor device manufacturing method may include the step of selecting a desired pattern among the plurality of patterns. In this case, the size difference is calculated for the selected pattern and the optimum exposure value is calculated using the size difference. Thus, the optimum exposure value for an important pattern, for example, can be calculated.
When the pattern is a developed pattern formed by development, the pattern size detection step includes the step of comparing the size of the developed pattern and a target value to calculate a size difference. When the pattern is an etched pattern formed by etching, the pattern size detection step includes the step of comparing the size of the etched pattern and a target value to calculate a size difference. In this case, similar effects to the case of the above described semiconductor manufacturing system can also be expected.
A semiconductor device of the present invention includes a portion which is formed by exposing a photosensitive material at an optimum exposure value calculated by using a size difference between the size of a pattern formed after photolithography and a target value as well as exposure value of an exposure device during photolithography, developing the photosensitive material after exposure, and performing an etching process by using the developed photosensitive material.
Since the etching process is performed by using a pattern (pattern of a photosensitive material, for example) which is formed by exposure at the optimum exposure value as described above, the pattern (pattern of a conductive layer or an insulation layer, for example) formed by the etching process can have a size very close to a design value.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.